Low-alloy steel containing boron for high-temperature use



Patented Aug. 10, 1954 LOW-ALLOY STEEL CONTAINING BORON FOR HIGH-TEMPERATURE USE Claude L. Clark, Canton, Ohio, assignor to The Timken Roller Bearing Company, Canton, Ohio, a corporation of Ohio No Drawing. Application August 28, 1952,

- Serial No. 306,958

1 .which possess a 1000-hour 4 Claims.

This invention relates to steels thatcombine desirable properties at normal temperatures With excellent high temperature properties.

Certain parts of jet engine and gas turbines,

- mium, from about 0.2 to 1.0 per cent of manganese, from about 0.25 to 1.0 per cent of molybdenum,

- from about 0.1 to 1.5 per cent of silicon, from about02 to 1.0 per cent of vanadium, and from such as their rotors, parts of aircraft super- 5. 0.0005 to 0.004 per cent of boron. The remainder chargers, and related devices operate at high ofthe steels consists of iron together with imstress and elevated temperatures. Various purities and elements in amounts that do not steels have been developed for such purposes, for adversely afiect the properties that characterize instance the Well-known steel alloy disclosed in the steels of, this invention. For full develop- United States Patent No. 2,398,702. In gene ment of those properties the steels should coneral, the steels used for such purposes up to tain not over about 0.04 per cent each of phosthe present time have been highly alloyed, and phorus and sulfur. it is characteristic of them that they are very Withinthe foregoing limits I now prefer that diflicult to fabricate, they require special heat the steels contain from about 0.20 to 0.35 per treatments of longduration and, insome in-v cent of carbon, from about 1 to 2 per cent of stances, are rather complicated, or because bechromium, from about 0.5 to 1.0 per cent of ing highly alloyed they are admin on strategic manganese, from about 0.4 to 0.6 per cent of metals. molybdenum, from about 0.5 to'1.0 percent of The present shortage of certain critical metals silicon, from about 0.7 to 0.9 per cent of vanadihas created the need for steels of low alloy congoum, and from 0.001 to 0.003 per cent of boron.

tent that are adapted to replace the highly alloyed steels used up to the present time for the foregoing and related purposes. In particular, there is a demand for steels containing a maximum of 5 per cent of alloying elements, rupture strength at F. in excess of 30,000 pounds per square inch (p. s. i.), and which also possess good ductility to fracture at 1100 F. Steels meeting this combination of requirements have not been 0 available heretofore.

It is among the objects of the invention to proture use having a satisfactory combination of high temperature properties, and particularly sections up to 2 inches Steeis of the foregoing composition are readfabricated by all hot forming operations such, for example, as forging, sheet rolling, and piercing into seamless tubes. Likewise, they can bewelded readily.

The best combination of strength and ductility at both room temperature and at 1100 F. is

developed by air cooling, or normalizing, the

steels from 1800 F. minimum, followed by temporing to about 302/365 Brinell. This heat treatment produces a martensitic structure. For the steels are normalized at 1800 F. and tempered at 1200 F. For a wide range of section sizes the best high temperature properties are developed by air cooling from a rupture strength at 1000 hours and 1100 F. of 3:? 1800 F. followed by tempering at 1200 F. to the 40,000, or more, pounds per square inch, coudesired hardness. pled with desirable ductility to fracture under ,The excellent properties of these steels and those conditions. the high degree of shock resistance that ey A further object is to provide steel articles in 40 possess at elevated temperatures are cha acaccordance with the foregoing object that like- .teristically exemplified by the properties f a wise possess desirable mechanical properties at ste l in accordance with the invention and com normal temperatures. taining 0.24 per cent of carbon, 1.33 per cent of Still another object is to provide steel articles chromium, 0.49 per cent of manganese, 0.52 embodying h foregoing Objects and whose per cent of molybdenum, about 0.65 per cent of p op t s are d v d y a simple a d s t a silicon, 0.89 per cent of vanadium, and 0.002 per heat treatment cent of boron. This steel when normalized from Yet another object is to provide steel articles 18090 E and tempered at 12900 R hadthe f in accordance with the foregoing objects conlowing room temperature properties; tar'ning not over about 5 per cent of alloy con- I tent, Tensile strength p. s. i 164,000 The invention is predicated upon my discovery 0.2% yield strength p. s. i 150,000 that its stated objects are attained with steel Elongation in 2" percent 16.5 containing from about 0.15 to 0.5 per cent of Reduction of area do 53.8 carbon, from about 0.75 to 2.5 per cent of chro- Brinell hardness 321/341 Furthermore, considering their low alloy content the steels of this invention possess unusually high rupture strength and ductility to fracture at failure. Thus the foregoing steel has a rupture strength of at least 40,000 p. s. i. in 1000 hours at 1100 F., while the ductility at fracture is 9.5 per cent. Surprisingly enough, the ductility is almost double that of a steel of essentially the same composition but containing no boron, the 1000 hour rupture strength at 1100 F. of which was 35,000 p. s. i., and the elongation at rupture 5.0 per cent.

Thus the steels of this invention containing exceedingly small amounts of boron are much more useful for work at 1100 F. than similar steels with no boron. And the range of boron stated is critical for when the boron content exceeds 0.005 per cent the high temperature (1100 F.) strength is impaired, and the hot working properties are likewise aifected adversely, so much so that at 0.01 per cent of boron the hot working temperature must be held below 2000 F. Moreover, when heat treated as described the products possess high tensile strength at room temperature, stress-rupture strength in 1000 hours at 1100 F. of at least 40,000 p. s. i. and elongation at rupture in excess of 9 per cent. In contrast, the same steels without this minute amount of boron when tested 1000 hours at 1100 F. have stress-rupture strength of only about 30,000 p. s. i., and about 5 per cent elongation at rupture.

The high temperature properties of these steels adapt them to the making of parts that are subjected to high stress at such high temperatures as 1100 F., and obviously they represent a major saving of critical alloying elements in comparison with the presently used alloy steels containing several times as much as alloy content as is present in these steels. The properties of these steels adapt them excellently for other purposes also, such as for aircraft brake discs.

This application is a continuation-in-part of my copending application Serial No. 246,159, filed September 11, 1951, now Patent No. 2,645,574.

According to the provisions of the patent statutes, I have explained the principle and mode of practicing my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. Steel adapted for operation at elevated temperatures up to at least 1100 F. which as normalized from about 1800 F. and tempered at 1200 F. to a hardness of 300 to 365 Brinell has room temperature tensile strength in excess of 160,000 pounds per square inch, and has a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture in excess of about 9 per cent, and having substantially the following composition: carbon 0.15 to 0.5 per cent, boron 0.0005 to 0.004 per cent, chromium 0.75 to 2.5 per cent, manganese 0.2 to 1 per cent, molybdenum 0.25 to 1 per cent, silicon 0.1 to 1.5 per cent, vanadium 0.2 to 1 per cent, and the remainder iron together with impurities. and ele- 4 ments in a total amount that does not impair the stated properties.

2. Steel adapted for operation at elevated temperatures up to at least 1100 E. which as normalized from about 1800 F. and tempered at 1200" F. to a hardness of 300 to- 365 Brinell has room temperature tensile strength in excess of 160,000 pounds per square inch, and a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture in excess of about 9 per cent, and having substantially the following composition: carbon 0.2 to 0.35 per cent, boron 0.001 to 0.003 per cent, chromium 1.0 to 2.0 per cent, manganese 0.5 to 1 per cent, molybdenum 0.4 to 0.6

per cent,.silicon 0.5 to 1.0 per cent, vanadium 0.7 to 0.9 per cent, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

3. A hot Worked and heat treated steel article for operation at elevated temperatures up to at least 1100 F., the article having been normalized from about 1800 F. and tempered at about 1200 F. to 300 to 365 Brinell and having room temperature tensile strength in excess of 160,000 pounds per square inch, a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture in excess of about 9 per cent, and having substantially the following composition: carbon 0.15 to 0.5 per cent, boron 0.0005 to 0.004 per cent, chromium 0.75 to 2.5 per cent, manganese 0.2 to 1 per cent, molybdenum 0.25 to 1 per cent, silicon 0.1 to 1.5 per cent, vanadium 0.2 to 1 per cent, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

4. A hot worked and heat treated steel article for operation at elevated temperatures up to at least 1100 F. the article having been normalized from about 1800 F. and tempered at about 1200 F. to 300 to 365 Brinell, and having room temperature tensile strength in excess of 160,000 pounds per square inch and a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture in excess of about 9 per cent, and having substantially the following composition: carbon 0.2 to 0.35 per cent, boron 0.001 to 0.003 per cent, chromium 1.0 to 2.0 per cent, manganese 0.5 to 1 per cent, molybdenum 0.4 to 0.6 per cent, silicon 0.5 to 1.0 per cent, vanadium 0.7 to 0.9 per cent, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain July 17, 1946 

1. STEEL ADAPTED FOR OPERATION AT ELEVATED TEMPERATURES UP TO AT LEAST 1100* F. WHICH AS NORMALIZED FROM ABOUT 1800* F. AND TEMPERED AT 1200* F. TO A HARDNESS OF 300 TO 365 BRINELL HAS ROOM TEMPERATURES TENSILE STRENGTH IN EXCESS OF 160,000 POUNDS PER SQUARE INCH, AND HAS A RUPTURE STRENGTH IN 1000 HOURS AT 1100* F. OF AT LEAST ABOUT 40,000 POUNDS PER SQUARE INCH AND ELONGATION AT RUPTURE IN EXCESS OF ABOUT 9 PER CENT, AND HAVING SUBSTANTIALLY THE FOLLOWING COMPOSITION: CABRON 0.15 TO 0.5 PER CENT, BORON 0.0005 TO 0.004 PER CENT, CHROMIUM 0.75 TO 2.5 PER CENT, MANGANESE 0.2 TO 1 PER CENT, AND THE REDENUM 0.25 TO 1 PER CENT, SILICON 0.1 TO 1.5 PER CENT, VANADIUM 0.2 TO 1 PER CENT, AND THE REMAINDER IRON TOGETHER WITH IMPURITIES AND ELEMENTS IN A TOTAL AMOUNT THAT DOES NOT IMPAIR THE STATED PROPERTIES. 